tc: fix parallel build file with lex/yacc

tc: fix parallel build file with lex/yacc

Building iproute2 in parallel might hit the race failure:
	emp_ematch.l:2:30: fatal error: emp_ematch.yacc.h:
		No such file or directory
	make[1]: *** [emp_ematch.lex.o] Error 1

This is because we currently allow the yacc/lex files to generate and
compile in parallel.  So add a simple dependency to make sure yacc has
finished before we attempt to compile the lex output.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>